The present invention relates to an optical recording medium onto which data is recordable and readable using a laser light source. The optical recording medium is useful as a recording medium with both higher data storage density and higher capacitance for recording a variety of information or pictures. More particularly, the present invention relates to an optical recording medium using a charge transfer complex. Data is recorded by irradiating a laser beam onto organic dyes formed in a recording layer wherein the dyes absorb the laser light and melt or decompose. Data is reproduced by reading the reflectivity difference between a recording portion and a non-recording portion. In accordance with the invention disclosed herein, cyanine-based dyes are applied in the optical recording medium by forming charge transfer complex (cyanine-TCNQ) with TCNQ (tetracyanoquinodimethane) or derivatives thereof as a recordable material and thereby remarkably improving a recording intensity.
Information recording media utilizing a high energy density beams, such as laser beams, have been developed in recent years and are put to practical use. Such recording mediums are called optical discs and their practical applications have been found, for example, as video discs and audio discs as well as disc memory for large-capacity computers and large-capacity static image files.
With the explosion of a variety of information in accordance with orientation toward an information-intensive society, recording media have been required to have increased data storage density and increased storage capacity. In response to this need, recording techniques known generally as magnetooptic recordings were developed. A magnetooptic recording medium is substantially high in data storage density. In addition, it is a non-contact write/read method, so that it is a relatively simple means for data storage, and it can enjoy longevity. However, there are many difficulties in the preparation of magnetooptic recording media, as magnetic materials of heavy metals are used and an expensive and complicated apparatus for vacuum deposition or sputtering is required.
Organic optical recording media using an organic dyes for recording material are increasingly employed as a promising alternative for data storage. Organic optical recording media are inexpensive and can be prepared using a simple process, (e.g. spin-coating). This organic optical recording medium is being watched with keen interest in the field of optical recording medium.
Relative to their operation, optical recording media include two types, that is, one capable of recording (or writing) information only once (i.e., WORM: write once read many type) and the other capable of recording and erasing information repeatedly (i.e., erasable type). Specifically, WORM type optical recording media of heat mode is used as a means for recording and reproducing data of images such as characters, diagrams, etc. or sound. Information on the WORM type optical recording medium is recordable only once by the user, and so is an appropriate recording medium for recording, storing and keeping information, in contrast to a compact disk-read only memory (CD-ROM) already has information recorded on it when it reaches the end user.
Among the organic dyes used in manufacturing the WORM type optical recording medium are cyanine-based and melocyanine-based dyes (Japanese Patent Laid-open Sho 63-179792), triarylmethane-based dyes, polymethine-based dyes (Japanese Patent Laid-open sho 58-194595), squarylium-based dyes, azulenium-based dyes (Japanese Patent Laid-open sho 64-71791 and 64-71792), phthalocyanine-based dyes (Japanese Patent Laid-open sho 58-77043, 55-97033, 57-212639 and U.S. Pat. No. 4,458,004), naphthoquinone-based dyes (Japanese Patent Laid-open sho 58-224793 and 63-233886), pirylium-based dyes (Japanese Patent Laid-open sho 62-163050 and U.S. Pat. No. 4,513,071), etc.
Among the above dyes, phthalocyanine-based dyes have poor recording sensitivity and low solubility, and so the dye layer should be prepared using deposition process in order to form the recording layer. Deposition of the naphthoquinone-based dyes is simple, but the formed layer has low reflectivity. Most of the dyes except the cyanine-based dyes are low in solubility In addition to low reflectivity. Accordingly, the cyanine-based dyes are most widely used although these dyes are unstable against light or heat. However, with cyanine-based dyes, a little dye may absorb the laser light in the desired wavelength region for recording and have good solubility to solvents so as to form the recording layer through solution coating.